We investigated the locomotor strategy following initial immersion in hatchling leatherback sea turtles, Dermochelys coriacea. From kinematic data, this strategy is divided into three phases : sinking, an intermediate phase involving attempts to elevate into the free water column, and finally an efficient elevation that permits emersion of the head to ventilate. From the resolution of water flows, hydrodynamical models of forces were calculated for the down- and upstroke phases of the fore limbs, the rearward and forward phases of the hind limbs. Efficient body elevation results from a complex mechanical process involving synchrony within the pairs of fore and hind limbs, integration between opposite phases of fore- and hind-limb cycles, generation of an efficient angle of attack, and body inclination. The main propulsive action is provided by the fore flippers on the downstroke at the beginning of the final, efficient elevation. As in horizontal swimming, fore flippers play the major role during first immersion, but the role of the hind limbs should not be ignored. |
